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A Roughing Filter is used to remove suspended solids from very turbid (or muddy) water using differently sized filtration media ranging from coarse to fine gravel. It is a pre-treatment step prior to a final disinfection process, such as Chlorination [T.6], Slow Sand Filtration [T.9] or Ultrafiltration [T.10]. It can be used in the stabilisation and recovery phases of an emergency.

Rapid Sand Filters use coarse sand as a filtration medium to remove fine suspended solids from water with varying levels of turbidity (or ‘muddiness’). It is a pre- treatment step prior to a final disinfection process, such as Chlorination [T.6], and can be used in all phases of an emergency.

Microfiltration (MF) membranes provide excellent filtration with low final water turbidity (typically less than 0.1 NTU) and high removal levels for pathogenic protozoan cysts/oocysts, Giardia and Cryptosporidium and bacteria. As a final treatment step, Chlorination [T.6] or Ultrafiltration [T.10] as well as Nanofiltration/Reverse Osmosis [T.15] can be used. MF is applicable in all emergency phases and at different scales (see [H.4] for household scale).

Sedimentation is a pre-treatment step used to remove suspended solids from water with varying levels of turbidity (or ‘muddiness’) and may involve the addition of chemicals to accelerate the process. It can be used prior to a final treatment step, such as Microfiltration [T.3], Chlorination [T.6] or Nanofiltration/Reverse Osmosis [T.15]. Sedimentation can be used in all phases of an emergency.

Assisted Sedimentation with Filtration is a pre-treatment step used to remove suspended solids from water with varying levels of turbidity (or ‘muddiness’) to prepare it for a final disinfection step, such as Chlorination [T.6]. It can be used in all phases of an emergency.

Chlorination is a final drinking water treatment step, as it inactivates pathogens such as bacteria and viruses. It is also used for other purposes such as disinfecting infrastructure (e.g. wells, pipes or boreholes) and equipment (e.g. in cholera treatment centres, [X.14]). It is used in all phases of an emergency.

Onsite Electro-Chlorination (electrolytic generation of sodium hypochlorite) produces chlorine for disinfection through the electrolysis of aqueous sodium chloride (common salt, or NaCl). It can be produced in batch mode, converting a salt solution into sodium hypochlorite with a concentration of 6–12 g/L either in one buffer tank or in a flow-through system that continuously produces hypochlorite.

Under correct design and operational conditions, Ultraviolet (UV) Light can have anti-bacterial and anti-viral properties and can destroy pathogenic organisms in nonturbid water.

Slow Sand Filters remove suspended solids and pathogens from water with varying levels of turbidity (or ‘muddiness’) using fine sand as the filtration medium. They are used as a final treatment step and are most applicable in the stabilisation and recovery phases of an emergency.

Ultrafiltration (UF) is part of the family of pressurised membrane filtration systems that can purify water from undissolved and most dissolved substances. UF is used as a final treatment step and can be applied in the acute response as well as in the stabilisation and recovery phases of emergencies.

Fluoride is a groundwater contaminant derived from minerals present in rocks and soils (commonly volcanic-derived sediments). At levels over 1.5 mg/L, it can directly impact human health so must be removed to ensure a safe water supply. Nonetheless, as the negative health impacts only occur over the long term and because they are time consuming to establish, Fluoride Removal processes are more suited to the stabilisation and recovery phases.

Arsenic is a groundwater contaminant derived from naturally occurring minerals present in rocks and soils (commonly in young alluvial sediments) as well as from industrial activities (e.g. mining). When present at levels over 10 μg/L, arsenic can directly impact human health and should be addressed as soon as possible at any phase of an emergency. Arsenic can be removed from groundwater by precipitation, adsorption, ion exchange or Reverse Osmosis [T.15].

Granular Activated Carbon (GAC) is the most used adsorption method in drinking water to remove taste, odour and colour-causing compounds, natural organic matter, disinfection by-products and synthetic organic chemicals present in the source water. GAC is also used for vapour treatment to remove noxious odours and contaminants. In small-scale treatment plants, it is often used for chlorine and chloramine removal. GAC can be used in all phases of an emergency.

Ozonation is a water treatment process that destroys microorganisms and degrades organic pollutants through the infusion of ozone, a gas produced by subjecting oxygen molecules to a high electrical voltage. During emergencies, the technology is mainly applicable in the stabilisation and recovery phases in urban contexts, where the experience in using such systems already exists.

Nanofiltration and Reverse Osmosis (NF/RO) have essentially the same equipment arrangements, and both remove contaminants by applying pressure to water across a semi-permeable membrane. RO is used to desalinate brackish water and seawater and removes organic and inorganic compounds (e.g. nitrate) and microorganisms. The key difference is that NF removes less salt (e.g. NaCl) and other monovalent ions than RO and is mainly used to remove colour, organic contaminants (e.g. pesticides) and lower the hardness (softening). Distillation, such as a solar still made of local materials, is a potential alternative. A related method, membrane distillation, is typically not commercially available.